Method of preparing sulfamic acids from organic isocyanates



ldETHOD OF PREPARING SULFAMIC ACIDS FROMORGANIC ISOCYANAIES Theodore I.Bieber, Kew Gardens, N. Y.

No Drawing. Application August 12, 19 53,

SerialNo'. 373,890

9 Claims. (Cl. 260-500) The present invention relates to a method ofpreparing sulfamic acids from organic isocyan ates and, moreparticularly, it relates to a method or" preparing sulfamic acids 'byreacting organic isocy anates with sulfuric acid or oleum.

I have found that if organic isocyanates cf the general formula (R)NCOor ON(.R")NCO, where R is any alkyl radical and R is any bivalentaliphatic hydrocarbon radical that are not readily sulfon'ated, sulfatedor oxidized under the reaction conditions, are treated with sulfuricacid or oleum, the corresponding sulfamic and di-sulfamic acids will beproduced in very satisfactory yield.

Accordingly, it is an object of the present invention to provide amethod of preparing monoand di-sulfa nic acids from correspondingorganic monoand di-isocyanates.

Another object of the present invention is to provide a noveldi-sulfarnic acid of a type never pr'oduced heretofore.

Other objects and advantages of the present invention will become moreapparent as it is described in detail below.

The novel process that I have discovered for forming the mono anddi-sulfamic acids may be generally represented by the following reactionwhere W is R when is equal to l and Wis R" when 1 is equal to 2, andwhere R and R" are alkyl and bivalent aliphatic hydrocarbon radicals,respectively, that are not readily sulfonated, sulfated, or oxidizedunder the reaction conditions.

With respect to the process for forming the monosulfamic acids, it maybe represented by the following equation where R is any alkyl radicalthat is not readily sulfon'ated, sulfated or oxidized under theconditions of the reaction.

The process for forming the di-sulfamic acid may be represented by theequation where R" is any bivalent aliphatic hydrocarbon radical that isnot readily sulfonated, sulfated or oxidized under the conditions of theprocess.

I have discovered that any sul-fonation, sulfation or oxidation of thealkyl or bivalent aliphatic hydrocarbon groups that may occur may becompletely eliminated or at least reduced to a minimum amount, if theprocess is carried out at the lowest temperature at which the evolutionof carbon dioxide occurs. To effect this, the process may be performedin an ice cooled vessel. However, higher temperatures may be employedwhere the alkyl or bivalent aliphatic hydrocarbon groups areparticularly in sensitive to sulfonation, sulfation or oxidation.

Although the above reactions may be carried out with 100% sulfuric acid,I prefer to employ oleum for the sake firm P ten 0..

q 2,785,196 .Eatpntss Me 2 of convenience. Additionally, I prefer anoleum with a low sulfur trioxide content rather than one with a highsulfur trioxide content because the sulfonating, sulfating and oxidizingability of oleum increases with an increase in sulfur trioxide content.Thus the possibility of undesired attack on the alkylor bivalentaliphatic hydrocarbon group is reduced ;by using an oleum oflow sulfurtrioxide content.

Concentrated sulfuric acid may also be employed for the above reactionsout it is noted that amine bisulfates are formed along with thesulfaniic acids. This is due to hydrolysis of the organic isocyanates bythe water contained in the concentrated sulfuric acid. Thus, it ispreferable to use sulfuric acid or oleum if 'sulfamic acids are to beobtained in high yields.

In order to isolate the sulfamic acids produced by my process, I dilutethe reaction mixture with a liquid in which the sulfamic'acid isinsoluble and in which the excess sulfuric acid or oleum is readilysoluble. Ether is such a liquid which I have found useful for thispurpose. I then filter the ether mixture to obtain the crystallinesulfamic acid.

Although the above ether filtration technique leaves the sulfami-c acidin a pure form, it may be necessary in some cases to recrystallize thesulfamic acids formed fro'm :a suitable solvent or solvent mixture. Ifthis recrystallization still does not suflice to obtain the sulfamicacids in pure form, I employ the use of lead oxide to purify theproduct.

Thelea-d oxide method comprises the steps of adding lead oxide to anaqueous solution of the sulfamic acid to be purified. Lead hydroxide andlead sulfate are filtered out of the solution. The filtered solutioncontaining the Water soluble lead salt of the sulfamic acid is treatedwith hydrogen sulfidefto precipitate lead sulfide. The lead sulfide isthen removed by filtration. 'Next, the filtrateis preferably evaporatedat reduced pressure and temperature (less than 100 C.) to avoidhydrolysis of the sulfamic acid. The remaining material will be purecrystals of the .sulfamic "acid.

' Below are several examples which illustrate my invention but do not inany way limit it thereto.

Example 1 To prepare ethyl sulfamic acid, 6.0 g. of ethyl isocyanatewere added dropwise to 70 g. of ice cooled and mechanically stirred 20%oleum. The reaction proceeded with the evolution of carbon dioxide. Awhite solid, which dis solved with bubbling, was noticed during thereaction. When one half of the isocyanate had been added, the ice bathwas removed and the reaction continued. After all the isocyanate wasadded, the reaction mixture was slightly lukewarm.

The chilled reaction mixture was poured slowly into 450 ml. of chilledanhydrous ether, which mixture was ice cooled and shaken during themixing. The precipitated ethyl sulfamic acid was collected on asintered-gl-ass tunnel and washed with ether. The ethyl sulfamic acidweighed 8.8 g. which represented an 83% yield. Also, it gave only a veryfaint test for sulfate ion.

To purify the product, it was dissolved in methanol and reprecipitatedby the addition of -a relatively large quantity of ether.

Example II The ethyl sulfamic acid formed in Example I was dissolved inwater. More than an equivalent amount of lead monoxide was added to thesolution. Excess lead hydroxide and lead sulfate were removed byfiltration. The filtrate, which contained lead ethylsulfamate, wastreated with hydrogen sulfide to precipitate lead sulfide. Afterfiltration to remove the lead sulfide, the filtrate wasdistilledat--reduced-pressure. The distilling bath did-not exceed-55 Q.The residual solid was dissolved in methanol and, on slow evaporation ofthe solvent, large crystals of ethyl sulfamic acid were obtained. Thesecrystals had a melting point of 170-171 C. a

This example of the lead oxide purification method need only be employedwhen there is heavy sulfate contamination of the sulfamic acid producedin accord with my invention. In the case of the sulfamic acid producedin Example I, it was not actually necessary. However, this example isgiven as an illustration of the lead oxide method.

Exampie III In order to form hexamethylenedisulfamic acid, 5.3 g. ofhexamethylene di-isocyanate were slowly added, to 22.4 g. of ice cooledand mechanically stirred oleum. It was noted that a white solid formedand carbon dioxide was evolved. After all the isocyanate was added tothe reaction mixture, gas evolution continued sluggishly in the cold. Inorder to carry the reaction to completion, the mixture was graduallyheated to 95 C., at which time no more gas was given ofi. it is possiblethat the second isocyanate group requires a higher reaction temperaturebecause of the low solubility of the substance formed in theintermediate stage.

The reaction mixture, which contained a finely divided solid, waschilled to 0 C. whereupon considerably more solid material wasprecipitated. The chilled mixture was added to 300 ml. of ice cooledether and filtered by suction. The filtered hexamethylenedisulfamic acidwas washed with ether. It was found to weigh 8.6 g., which was 98.9% oftheoretical yield.

Complete removal of sulfate ion was not achieved even though the productwas dissolved in methanol and re precipitated by ether. Accordingly, thelead oxide puriiication method described in Example II was employed toobtain sulfate free hexamethylenedisulfamic acid.

While the invention has been described in detail and prises mixing analkyl isocyanate with a sulfonating agent which is at least about H2804,and maintaining a temperature at which evolution of carbon dioxideoccurs, whereby alkyl sulfamic acid is formed.

2. A method of forming sulfamic acids which comprises mixing an alkylisocyanate wih a sulfonating agent which is at least about'100% H2804,and maintaining a temperature at which evolution of carbon dioxideoccurs, whereby alkyl sulfamic acid is formed, then diluting thereaction mixture with a liquid in which said sulfamic acid is insolubleand said sulfuric acid is soluble and recovering said sulfamic acid.

3. A method of forming sulfamic acids which comprises introducing withstirring small amounts of an alkyl isocyanate into a body of asulfonating agent which is at least about 100% H2804, and maintaining atemperature at which evolution of carbon dioxide occurs, whereby alkylsulfamic acid is formed.

4. A method of forming sulfamic acids which comprises inmixing an alkylisocyanate with a sulfonating agent which is at least about 100% H2804,and maintaining a temperature at which evolution of carbon dioxideoccurs by cooling the reaction mixture below room temperature, wherebyalkyl sulfamic acid is formed.

5. A method of forming sulfamie acids which comprises mixing an alkylisocyanate with a sulfonating agent which is sulfuric acid containingexcess S03, and maintaining a temperature at which evolution of carbondioxide occurs, whereby alkyl sulfamic acid is formed.

6. A method according to claim 1 in which the isocyanate is a monoalkylisocyanate.

7. A method according to claim 1 in which the isocyanate is an aliphaticdi-isocyanate.

8. A method according to claim 1 in which the isocyanate is ethylisocyanate.

9. A method according to claim 1 in which the isocyanate ishexamethylene di-isocyanate.

References Cited in the file of this patent Traube et al.: Berichte,vol. 53, PP. 1493-1501 (1920).

Linhardz. Justus Liebigs Annalen der Chemie, vol. 535, pp. 267-284(1938).

Audrieth et al.: Chemical Reviews, vol. 26 (19 39), p. 58.

Noller: Chemistry of Organic Compounds, p. 302 (1954), reprint,Copyright 1951.

2. A METHOD OF FORMING SULFAMIC ACIDS WHICH COMPRISES MIXING AN ALKYLISOCYANATE WITH A SULFONATING AGENT WHICH IS AT LEAST ABOUT 100% H2SO4,AND MAINTAINING A TEMPERATURE AT WHICH EVOLUTION OF CARBON DIOXIDEOCCURS, WHEREBY ALKYL SULFAMIC ACID IS FORMED, THEN DILUTING THEREACTION MIXTURE WITH A LIQUID IN WHICH SAID SULFAMIC ACID IS INSOLUBLEAND SAID SULFAMC ACID IS SOLUBLE AND RECOVERING SAID SULFAMIC ACID.